A Gas-Emission Crater in the Erkuta River Valley, Yamal Peninsula: Characteristics and Potential Formation Model

Abstract

Methane is a powerful greenhouse gas, and the abrupt degassing events that recently have formed large craters on the Russian Arctic Yamal and Gydan Peninsulas have caused major concern. Here we present field data on cover sediments and evolution of a gas-emission crater discovered in the Erkuta–Yakha River valley in the southern Yamal Peninsula in June 2017. The crater is located south of other similar craters discovered over the past decade in northern West Siberia. Data were collected during a field trip to the Erkuta crater in December 2017 which included field observations and sampling of permafrost soil and ground ice from the rim of the crater. All soil and ice samples were measured for contents of methane and its homologs (ethane and propane) and carbon dioxide. The contents of carbon dioxide in some samples are notably higher than methane. The strongly negative δ13С of methane from ground ice samples (−72‰) is typical of biogenic hydrocarbons. The ratio of methane to the total amount of its homologs indicate a component of gases that have migrated from a deeper, thermogenic source. Based on obtained results, a potential formation model for Erkuta gas-emission crater is proposed, which considers the combined effect of deep-seated (deep gas migration) and shallow (oxbow lake evolution and closed talik freezing) causes. This model includes several stages from geological prerequisites to the lake formation.

Evidence of Gas Emissions from Permafrost in the Russian Arctic

“…The carbon isotope composition of methane from ground ice in the crater wall (-72‰ PDB δ 13 С) indicates a biogenic origin of permafrost methane. Apart from methane, its homologs (ethane and propane) were presented in the gas samples, which demonstrates the possibility of catagenic gas participation in crater formation [26]. The Seyakha crater was discovered 33 km north of Seyakha Village soon after an event of spontaneous ignition and explosion of gas on 28 June 2017.…”

“…The review of published evidence on deep gas-emission craters (Figure 1), along with our field and laboratory data [26], allows a number of inferences: − In the witnessed cases, gas release was accompanied by explosions and fire; − All gas analyses showed the presence of methane; − Many of the gas-emission events were preceded by heaving that produced meters high mounds; − All discovered craters were round in shape but differed in size and depth, up to tens of m; − In all cases, rocks around the craters contained ground or pore ice evident in the crater walls or in the ejected fragments; − Most of the craters were encircled by parapets of ejected rock and soil; rock fragments were dispersed to distances of 100 m or farther around; − Most of the craters became filled with water and transformed into lakes in two or three years after the emission event.…”

“…People of the Center reported heaving and rupture of the previously flat surface a year before the crater discovery. The crater is located south of all other such features known in northern West Siberia [26]. When it was found, the crater had a diameter of ~10-12 m and a depth of 20 m ( Figure 5).…”

“…More than 10 gas-emission craters encircled with ridge-like parapets of ejected ground resulting from explosive events (cryovolcanism) have been found so far in the Yamal, Gydan, and Taymyr Peninsulas in northern Siberia (Table 1) [19,22,[24][25][26]. Cryovolcanism of this kind became first known to the international scientific community in 2014, when a 70 m deep crater (Yamal Crater) [22,[44][45][46][47][48][49] was discovered 30 km south of the Bovanenkovo field, 5 km away from the Bovanenkovo-Ukhta gas pipeline.…”

“…Active gas emission from the Arctic permafrost was observed during gas surveys of the near-surface atmosphere [8,11], the active layer, and water bodies [10,[12][13][14][15][16][17][18][19]. Crater features on the surface record explosive emission of deep methane [20][21][22][23][24][25][26].…”